The present invention relates to a device for position and/or length determination.
Such devices are used in particular in an industrial context for length measurement, for instance typically in connection with ascertaining movements of or lengths traveled by a machine tool or in corresponding measurement tasks in a materials-handling or conveying system.
Such length measurement systems typically have a carrier unit which is provided with a magnetic length coding. Such a length measurement device is known, for example, from the German utility model 200 12 703 by the Applicant.
Also known from the prior art are devices which have an absolute magnetic coding, and by way of example reference should be made to German patent application 197 32 713 by the Applicant.
Compared to relatively coded systems, such absolute codings have the advantage that end or reference positions do not have to be detected; rather, the position along the carrier unit with the length coding can be found directly from a current position of a sensor head.
However, such devices which are known from the prior art and are considered to be generic have the disadvantage that, in order to achieve an absolute magnetic length coding, typically at least two parallel tracks of the length coding have to be provided in order to form a useful length resolution for the desired absolute coding. As a result, however, on the one hand the carrier unit is problematic to produce (and in particular is still not very suitable for curved carrier units provided with the length coding), and also the sensor head that cooperates with the magnetic length coding is bulky and difficult to handle and is thus potentially difficult to guide and control.
A further disadvantage of absolute codings, particularly those which are generated by means of a so-called random code or pseudo-random code, is that, on account of a relatively asymmetric distribution of coding sections magnetized with the respective polarity, magnetization inhomogeneities may occur, particularly with regard to a so-called intersymbol interference (the magnetic signal of smaller poles is impaired by adjacent large areas, that is to say a number of areas having identical poles) . This in turn adversely affects the reading reliability of the carrier unit.
However, in industrial production, reliability and freedom from interference are of great importance, and thus there is a need for considerable simplification and improvement in this respect.
It is therefore an object of the present invention to improve a generic device for position and/or length determination comprising a carrier unit with an absolute magnetic length coding in such a way that it can be implemented in a simpler and more compact manner than known generic devices but at the same time allows a high (or even improved) length resolution and in particular can also be read reliably and in a manner unaffected by magnetic overlap effects, even under difficult operating conditions and at a distance from the carrier unit.